Optical Delay Module for Lengthening the Propagation Path of a Light Beam and Pulse Multiplication or Elongation Module

ABSTRACT

The invention relates to an optical delay module for lengthening the propagation path of a light beam comprises a first spherical mirror and a second spherical mirror, the first spherical mirror and the second spherical mirror having equal radii of curvature, the first and the second mirror being arranged on a common axis of symmetry with concave sides of the first and second mirrors being situated opposite one another at a distance from one another which corresponds to the radii of curvature of the first and second mirrors. The module also includes a coupling-in area for coupling the light beam into a space between the first and second mirrors and a coupling-out area for coupling the light beam out of the space between the first and second mirrors. The propagation path of the light beam between the coupling-in area and the coupling-out area corresponding at least approximately to quadruple the mirror distance, at least one optical arrangement arranged between the first and second mirrors, the optical arrangement being arranged to transfer the light beam between the first and second mirrors in such a way that the propagation path of the light beam without masking out of beam parts between the coupling-in area and the coupling-out area corresponds approximately to 2N times the mirror distance, where N is an integer &gt;2.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority of provisional U.S. patentapplication with Ser. No. 60/529,721 filed on Dec. 15, 2003.

FIELD OF THE INVENTION

The invention relates to an optical delay module for lengthening thepropagation path of a light beam.

The invention furthermore relates to an optical pulse multiplication orelongation module, having at least one beam splitter area, and having atleast one beam combining area, and having an optical delay module of theaforementioned type.

BACKGROUND OF THE INVENTION

A delay module and also a pulse multiplication or elongation module aredisclosed in the document U.S. Pat. No. 5,661,748.

Delay modules and pulse multiplication or elongation modules of thistype are used for example in optical beam guiding systems forsemiconductor lithography. By way of example, excimer lasers thatgenerate pulsed laser light are used as light sources in semiconductorlithography. Lasers of this type generate temporally short laser pulses,the individual length of which is approximately a few 10 ns, while theenergy of the individual laser pulses is usually greater than 5 mJ. Thismeans that the power density of the laser light is very high over theduration of an individual pulse.

These high power densities can damage downstream optical systems, forexample a lithography system, or the optical components of a beamguiding system or at least shorten the service life thereof.

In order to solve the problem of the high peak powers within a laserpulse, it has therefore been proposed to divide the light beam comingfrom the laser into two partial beams by means of a beam splitter deviceand to allow one partial beam to pass through a delay module andsubsequently to recombine the non-delayed light beam and the delayedlight beam. In this way, it is possible to increase the pulse durationof the laser pulses, or to split each laser pulse into a plurality oftemporally offset subpulses in order thus to lower the power density ofeach individual pulse or to reduce the peak power of the individualpulses.

The light beam generated by the laser naturally has a divergence, whichhas to be taken into account in pulse multiplication or elongationmodules. In the case of a propagation path difference between thedelayed partial beam and the non-delayed partial beam of several metersto a few tens of meters, the divergence of the light beam has the effectthat the delayed partial beam has a significantly larger cross sectionthan the non-delayed partial beam. This may have the effect that part ofthe light is masked out at the periphery of the light beam by opticalsystems arranged downstream and can thus no longer be used.

Furthermore, it is desirable for the delayed partial beam and thenon-delayed partial beam or the subpulses and the original pulse all tolie on one optical axis and, as already mentioned, to have identicalbeam properties.

In previous delay modules and pulse multiplication or elongationmodules, use is made of imaging optics that image the input of the delaymodule 1:1 onto the output of the delay module.

In the case of a delay module and pulse multiplication or elongationmodule disclosed in the document EP 1 069 453 A2 the detour line isformed by a plurality of plane mirrors, a refractive imaging optic inthe form of a slightly detuned Kepler telescope being used as imagingoptic for a 1:1 imaging of the input onto the output of the module. Anarrangement comparable therewith is disclosed in the document U.S. Pat.No. 6,549,267 B1.

Such a pulse multiplication or elongation module has the disadvantagethat the delay module requires a correspondingly large number of mirrorsand optical imaging elements which all have to be separately adjustedexactly and, in addition, be correspondingly held mechanically. Thismakes the optical system complex, which leads to considerable costs inthe production of the system and a considerable expenditure of time inadjusting the system.

In principle, in the case of the pulse multiplication or elongationmodule in accordance with the document U.S. Pat. No. 5,661,748 alreadycited in the introduction, this problem is avoided in principle by thedelay module having two spherical mirrors, the radii of curvature ofwhich are identical, and which are arranged on the common axis ofsymmetry with their concave sides situated opposite one another at amirror distance from one another which approximately corresponds to theradius of curvature of the mirrors.

Through the use of two confocal spherical mirrors, the refractiveimaging optic present in the known system mentioned previously can bedispensed with since the spherical mirrors already ensure a 1:1 imagingof the coupling-in area onto the coupling-out area.

In the case of this known pulse multiplication or elongation module, abeam splitter having alternately reflective and transmissive regions isused for coupling the light beam into the space between the twospherical mirrors. In this way, from the light beam coming from thelaser, a totality of first beam parts spaced apart from one another aretransmitted and a totality of second beam parts are coupled into thedelay module. The totality of the coupled-in beam parts circulate fourtimes in total between the two spherical mirrors and are then slightlyaxially offset by a beam offset plate in order then to be coupled outfrom the delay module by the beam splitter having the alternatetransmissive and reflective sections. The delay of the totality of thecoupled-in partial beams with respect to the totality of thenon-coupled-in partial beams is thus essentially limited to quadruplethe distance. In principle, although it would be possible to obtaingreater delay lengths, further and further beam parts would always bemasked out in this case, with the result that, given multiple completecirculation cycles, the light intensity decreases rapidly or the shapeof the light beam is altered.

Moreover, owing to the alternately transmissive and alternatelyreflective beam splitter or coupling-in element, the known delay moduleand pulse multiplication or elongation module are tolerance-sensitivebecause the special beam splitter has to be adjusted exactly in relationto the offset plate, which disadvantageously increases the adjustmentoutlay of this known system.

SUMMARY OF THE INVENTION

The invention is based on the object of developing a delay module and apulse multiplication or elongation module of the types mentioned in theintroduction to the effect that, with a compact design, it is possibleto realize large delay distances and the adjustment outlay of the systemis as low as possible in this case.

According to an aspect of the invention, an optical delay module forlengthening the propagation path of a light beam comprises a firstspherical mirror and a second spherical mirror, the first sphericalmirror and the second spherical mirror having equal radii of curvature,the first and the second mirror being arranged on a common axis ofsymmetry with concave sides of the first and second mirrors beingsituated opposite one another at a mirror distance from one anotherwhich corresponds to the radii of curvature of the first and secondmirrors, a coupling-in area for coupling the light beam into a spacebetween the first and second mirrors, and a coupling-out area forcoupling the light beam out of the space between the first and secondmirrors, the propagation path of the light beam between the coupling-inarea and the coupling-out area corresponding at least approximately toquadruple the mirror distance, at least one optical arrangement arrangedbetween the first and second mirrors, the optical arrangement beingarranged to transfer the light beam between the first and second mirrorsin such a way that the propagation path of the light beam withoutmasking out of beam parts between the coupling-in area and thecoupling-out area corresponds approximately to 2N times the mirrordistance, where N is an integer >2.

According to another aspect of the invention, a pulse multiplication orelongation module is provided, comprising an optical delay module asmentioned before.

According to another aspect of the invention, a semiconductorlithography system is provided, comprising an optical delay moduleand/or a pulse multiplication or elongation module as mentionedaccording to one of the afore-mentioned aspects of the presentinvention.

The optical arrangement present, according to the invention, between thetwo spherical mirrors may be realized by reflective and/or refractiveelements that have the effect that the light beam coupled into the delaymodule passes back and forth more than four times between the twospherical mirrors. According to the invention, it is thus possible torealize delay lengths of a multiple of double the mirror distance, forexample the mirror distance times six, times eight or more. The delaymodule according to the invention is tolerance-insensitive and thusconvenient for adjustment. Moreover, it is always ensured that thecoupled-in light beam is imaged 1:1 onto the coupled-out light beam,this being ensured by the two spherical mirrors spaced apart by thedistance of their radius. The delay module according to the invention isof very compact construction, the maximum dimension being determined bythe fixed distance between the two spherical mirrors. In combinationwith a beam splitter area and a beam combining area, it is possible,with the delay module according to the invention, correspondingly toprovide a compact, adjustment-insensitive pulse multiplication orelongation module.

In preferred refinements, which can be employed alternatively orcumulatively, the optical arrangement transfers the coupled-in lightbeam in such a way that the light beam is reflected at the first and thesecond mirror at in each case at least three different locations. Theoptical arrangement may preferably transfer the light beam in such a waythat the light beam is reflected at each mirror at at least threedifferent locations which lie on a straight line, or at at least threedifferent locations which do not lie on a straight line. Athree-dimensional beam folding is achieved in the latter case.

Generally, the optical arrangement preferably has optically active areaswhich axially offset the light beam at least once with reversal of thepropagation direction of the light beam, and/or which transfer the lightbeam at least once with maintenance of the propagation direction in anaxially offset manner.

With the optical delay module according to the invention, it ispossible, in particular, to utilize the entire area of the two sphericalmirrors for the beam folding, which is achieved by means of the opticalarrangement provided according to the invention.

In a preferred refinement, the optical arrangement of the delay modulehas at least two reflective areas which are arranged relative to oneanother in such a way that the light beam is retroreflected with anaxial offset.

This may be realized, in a preferred refinement, by virtue of the factthat the at least two at least partially reflective areas are at anangle of approximately 90° with respect to one another.

Such an optical arrangement creates a delay module whose delay length isapproximately eight times the mirror distance; that is to say, with onlytwo reflective areas that are at an angle of approximately 90° withrespect to one another, it is possible to double the delay length incomparison with the known delay module.

It is particularly preferred for the optical arrangement to have atleast one 90° prism whose two catheti have reflective areas.

The particular advantage of this measure consists in the fact that theoptical arrangement for obtaining a delay length that correspondsapproximately to eight times the mirror distance requires only oneoptical component, the further advantage consisting in the fact that the90° angle of the two reflective areas is fixed and does not require anyadjustment.

In this case, it is furthermore preferred for the hypotenuse of theprism to be perpendicular to the incident and emerging light beam.

In this case, it is advantageous that the light beam incident oremerging through the hypotenuse is not refracted at the hypotenuse, withthe result that beam deflection on account of refraction does not occur.

As an alternative to a prism having retroreflective properties, the atleast two reflective areas may also be formed by at least two mirrors.

Furthermore, it is preferred for the coupling-in area to be formed bythe rear side of one reflective area and/or for the coupling-out area tobe formed by the rear side of the at least one second reflective area ofthe optical arrangement.

This measure has the advantage that the optical arrangement comprisingthe at least two reflective areas at the same time can also perform thefunction of coupling the light beam coming from the laser into the delaymodule and coupling the delayed light beam out of the delay module, as aresult of which the number of optical elements and thus the costs andthe adjustment outlay of the delay module can be reduced further. By wayof example, in connection with one of the aforementioned refinements,the 90° prism may have the coupling-in area and coupling-out area at theouter sides of the two catheti.

In a further preferred refinement, the optical arrangement has at leastfour reflective areas, in each case two of the reflective areas beingarranged with respect to one another in such a way that theyretroreflect the light beam with an axial offset.

This refinement is suitable for the use of the delay module in the pulsemultiplication or elongation module in particular when the beam splitterarea or beam combining area is intended to coincide with the coupling-inarea or the coupling-out area. In other words, the beam splitter area orthe beam combining area can then be arranged between the two sphericalmirrors and thus be integrated directly in the delay module.

In this connection, the optical arrangement may preferably have two 90°prisms whose in each case two catheti form the in each case two areas tobe reflected, the prisms being arranged with their 90° angles facing oneanother, or the optical arrangement may equally also have a doubleretroprism through which the light beam passes twice, namely once on anoutward path and once on a return path, the double retroprism beingformed in such a way that the light beam is retroreflected on theoutward path and the return path in each case with an axial offset.

The latter refinement of the optical arrangement with at least onedouble retroprism again has the advantage that the four reflective areasare integrated in a single component in fixed spatial assignment to oneanother, which once again minimizes the cost and adjustment outlay.

In all of the aforementioned preferred refinements, the at least tworeflective areas are arranged in a plane outside a plane containing theaxis of symmetry of the first and second mirrors.

In this case, it is advantageous that the light beam is folded betweenthe two spherical mirrors along its delay distance in a plurality ofplanes and, as a result, the at least two reflective areas which arearranged in only one plane do not obstruct the beam path between the twospherical mirrors during multiple circulation of the light beam betweenthe two mirrors.

Alternatively or cumulatively to the refinement of the opticalarrangement with at least two reflective areas, it is likewise preferredfor the optical arrangement to have at least two refractive areasthrough which the light beam is axially offset upon passing through.

In this case, it is particularly preferred for the optical arrangementto have at least four refractive areas, of which two opposite sides ineach case are parallel to one another. By way of example and preferably,the four refractive areas may be the surfaces of a parallelogram-typeprism, the light beam passing through said prism twice, the light beambeing axially offset both times, the axial offset brought about in thecourse of passing through the first time being reversed in the course ofpassing through the second time.

The axial offset need not necessarily be the same for each passage ofthe light beam, but rather can be adapted when the delay module is usedin the pulse multiplication or elongation module in such a way as tocompensate for an offset through the beam splitter area, by way ofexample.

Furthermore, it is preferred for at least individual ones of therefractive areas to be arranged at the Brewster angle with respect tothe light beam.

In this case, it is advantageous that reflection losses at therefractive areas are minimized, with the result that it is possible todispense with reflection-reducing coatings of the refractive areas.

Furthermore, it is possible to realize a sequential arrangement of aplurality of optical arrangements with the just two spherical mirrors ofthe delay module. By way of example, given a mirror distance of 2 m, itis possible to realize an 8 m delay in combination with a 16 m delaywith just two prisms, two beam splitters and the two spherical mirrors.In this way, by way of example, a 30 ns pulse can be elongated to morethan 140 ms. By inserting further elements, even significantly greaterdelays or pulse elongations are possible solely by means of the twospherical mirrors. A plurality of pulse multiplication or elongationmodules can also be used sequentially.

In this case, the entire arrangement can be accommodated in a compacttube having a small diameter that is only slightly larger than thediameter of the light beam.

The optical delay module according to the invention and/or the opticalpulse multiplication or elongation module according to the invention ispreferably used in a semiconductor lithography system for producingsemiconductors.

Further advantages and features are apparent from the description belowand the accompanying drawing.

It goes without saying that the features mentioned above and featuresyet to be explained below can be used not only in the respectivelyspecified combination, but also in other combinations or by themselves,without departing from the scope of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the invention are illustrated in the drawingand are described in more detail hereinafter with reference thereto. Inthe figures:

FIGS. 1 a) to c) show an optical delay module as a basic module, FIG. 1a) showing the delay module with the beam path in side view,

FIG. 1 b) showing the delay module in perspective, and

FIG. 1 c) showing the delay module in section perpendicular to the axisof symmetry;

FIGS. 2 a) to d) show the delay module in FIG. 1 with an additionaloptical arrangement for beam transfer, FIG. 2 a) showing the delaymodule in side view, FIG. 2 b) showing the delay module in side viewrotated through 90° relative to FIG. 2 a) (plan view), FIG. 2 c) showingthe delay module in perspective and FIG. 2 d) showing the delay modulein cross section perpendicular to the axis of symmetry;

FIGS. 3 a) to 3 d) show a pulse multiplication or elongation module onthe basis of the delay module in FIG. 1 with an optical arrangement forbeam transfer that is modified relative to FIG. 2, FIGS. 3 a), b), c)and d) corresponding to the views of FIGS. 2 a), b), c) and d);

FIG. 4 shows a pulse multiplication or elongation module on the basis ofthe delay module in FIG. 1 with a further modified optical arrangement,FIG. 4 a) being a side view and FIG. 4 b) being a cross-sectionalillustration perpendicular to the axis of symmetry;

FIG. 5 shows an embodiment equivalent to FIG. 4 in a cross-sectionalillustration perpendicular to the axis of symmetry;

FIG. 6 shows the optical arrangement of the delay module in FIG. 4 a) inisolation;

FIG. 7 shows a further optical arrangement for use in a delay module andpulse multiplication or elongation module in isolation;

FIG. 8 shows a further embodiment of a delay module and pulsemultiplication or elongation module in a cross-sectional illustrationperpendicular to the axis of symmetry; and

FIG. 9 shows a pulse multiplication or elongation module comprising acombination of a delay module and an external beam splitter device.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 1 a) to c) illustrate an optical delay module 10 for lengtheningthe propagation path of a light beam 11. The light beam 11 is generatedfor example by a laser (not illustrated).

The delay module has a first spherical mirror 12 and a second sphericalmirror 14. The radii r₁ and r₂ of curvature of the mirrors 12 and 14 areidentical.

The first mirror 12 and the second mirror 14 are arranged on a commonaxis 16 of symmetry with their concave sides situated opposite oneanother, to be precise at a mirror distance D corresponding to the radiir₁ and r₂ of curvature. The arrangement is thus a confocal or 4farrangement of the mirrors 12 and 14, with the result that thisarrangement has the properties of a 1:1 imaging optic.

The delay module has a coupling-in area 18, which is completelyreflective if the delay module is not intended to serve autonomously aspulse multiplication or elongation module. The coupling-in area 18 isformed for example by a mirror tilted by 45° with respect to theincident light beam 11.

The coupling-in area 18 serves for coupling the light beam 11 into thespace between the first and second mirrors 12, 14.

Starting from the coupling-in area 18, the beam path is as follows. In amanner corresponding to the arrows depicted in FIG. 1 a), the light beam11 passes in the coupling-in area 18 to the location a at the secondmirror 14, is reflected there and passes approximately through the focalpoint F to the first mirror 12 and is reflected there at the location b.From the location b, the light beam passes to the second mirror 14again, is reflected there at the location c and once again passesapproximately through the focal point F to the first mirror 12, wherethe light beam is then reflected at the location d. From there the lightbeam 11 passes to the rear side of the coupling-in area 18, which isformed in reflective fashion and serves as coupling-out area 20 forcoupling the light beam 11 out of the space between the two mirrors 12and 14. In accordance with arrow 22, the light beam 11 thus leaves thedelay module 10 after four circulations, the coupled-out light beam 11and the coupled-in light beam 11 lying on the same optical axis andhaving the same shape and cross-sectional area since the delay module10, through the use of the spherical mirrors 12 and 14, images thecoupling-in area 18 1:1 onto the coupling-out area 20. The propagationpath of the light beam 11 has thus been lengthened in the delay module10 by approximately quadruple the mirror distance d.

The delay module 10 may also be used as pulse multiplication orelongation module if the coupling-in area 18 is only partly reflective,so that the light beam 11 incident on the coupling-in area 18 is partlycoupled into the delay module 10 and is partly transmitted. That partialbeam of the light beam 11 which has then circulated four times betweenthe mirrors 12 and 14 as described above is then combined with theincident light beam 11 at the coupling-out area 20, which then acts asbeam combining area. In this way, light pulses of which the light beam11 may be composed are elongated approximately four-fold or quadrupled,as a result of which the peak power of each individual pulse is reduced.

The illustration in FIG. 1 c) shows that the light beam is reflected atthe first mirror 12 at the two locations d and b, these two spots lyingin a plane that passes through the axis 16 of symmetry. The sameconditions are present at the mirror 14.

In the exemplary embodiments below, using the delay module 10, which mayalso be referred to as a basic module, a description is given of delaymodules and pulse multiplication or elongation modules by means of whichlarger delay paths can be achieved.

For this purpose, optical arrangements are introduced between themirrors 12 and 14, which transfer the light beam 11 between the mirrors12 and 14 in such a way that the propagation path of the light beam 11between the coupling-in area 18 and the coupling-out area 20 correspondsapproximately to 2 N times mirror distance D, where N is an integer >2.

FIGS. 2 a) to d) illustrate a delay module 30, which is based on thedelay module 10 and has the mirrors 12 and 14 in accordance with theexemplary embodiment in FIG. 1.

Furthermore, the delay module 30 has an optical arrangement 32, whichbrings about the aforementioned beam transfer.

The optical arrangement 32 has two reflective areas 34 and 36, which areat an angle of 90°0 with respect to one another.

The reflective areas 34 and 36 are formed by the catheti of a 90° prism38, but could also be replaced simply by two reflective mirrors arrangedat 90° with respect to one another.

The two reflective areas 34 and 36 form a retroreflective arrangement.

The reflective areas 34 and 36 are arranged in a plane 40 arrangedoutside a plane containing the axis 16 of symmetry of the mirrors 12 and14.

The coupling-in area 18 of the delay module 30 is formed by the rearside of the reflective area 34, and the coupling-out area 20 is formedby the rear side of the reflective area 36, with the result that thereflective areas 34 and 36 and also the coupling-in area 18 and 20 areall provided on just one optical component, namely the prism 38.

The beam path in the delay module 30 is as follows in accordance withFIG. 2 c) (also cf. the arrows in FIG. 2 a).

The incident light beam 11 is reflected at the coupling-in area 18 andpasses to the location a at the first mirror 12. From the location a,the light beam passes to the diametrically opposite location b of thesecond mirror 14, is reflected there and passes to the opposite locationc at the first mirror 12. From there the light beam is reflected to thelocation d at the second mirror 14. From there the light beam 11 passesto the reflective area 34, from there to the reflective area 36 and iscorrespondingly retroreflected with an axial offset. The light beam 11is thus transferred in the plane 40, i.e. in a plane that does not passthrough the axis 16 of symmetry of the mirrors 12 and 14. From thereflective area 36, the light beam passes to a location e at the secondmirror 14, is reflected from there to a location f at the first mirror,and passes from there to a location g at the second mirror 14. From thelocation g, the light beam 11 passes to a location h, is once againreflected there and impinges on the coupling-out area 20, from which thelight beam 11 then leaves the delay module 30.

By means of the optical arrangement 32, the light beam 11 is thus foldedthree-dimensionally in the delay module 30, that is to say that thelight beam 11 impinges on the mirrors 12 and 14 at the locations a to hwhich do not lie on a straight line (cf. FIG. 2 c), as is the case inthe delay module 10 in FIG. 1.

With the delay module 30 in FIG. 2, the delay distance thus amounts toapproximately eight times the mirror distance D.

By means of the arrangement—chosen in FIG. 2—of the prism 38 with thereflective areas 34 and 36 and the coupling-in area 18 and thecoupling-out area 20, the light beam 11, during its multiplecirculations between the mirrors 12 and 14, may pass the prism 38 partlyunimpeded, as is apparent from FIGS. 2 b) and 2 d).

FIGS. 3 a) to 3 d) illustrate a pulse multiplication or elongationmodule 50, which is based on a delay module 52, the optical arrangement54 of which is modified compared with the delay module 30 in FIG. 2.

The optical arrangement 54 of the delay module 52 has a total of fourreflective areas 56, 58 and 60, 62.

The reflective areas 56 and 58 are at an angle of 90° with respect toone another, as are the reflective areas 60 and 62. The reflective areas56 and 58 are formed by the catheti of a first prism 64, while thereflective areas 60 and 62 are formed by the catheti of a second prism66.

At the pair of reflective areas 56 and 58 and also at the pair ofreflective areas 60 and 62, the light beam 11 is in each caseretroreflected with an axial offset.

The two prisms 64 and 66 are arranged, in a manner similar to theexemplary embodiment in accordance with FIG. 2, in a plane lying outsidethe plane that contains the axis 16 of symmetry of the mirrors 12 and14, as revealed in FIG. 3 b).

The two prisms 64 and 66 are arranged in such a way that their 90°angles face one another, as revealed in FIG. 3 a).

In the case of this exemplary embodiment, the coupling-in area 18 of thedelay module 52 is formed by a beam splitter area 68, which partlycouples the incident light beam 11 into the delay module 52 and partlytransmits it without reflection at the mirrors 12 and 14 in accordancewith arrow 22.

The coupling-out area 20 simultaneously forms a beam combining area 70.In this way, that partial beam which is delayed by multiple circulationin the delay module 52 is combined with the non-delayed partial beam inaccordance with arrow 22 at the coupling-out location, the delayedpartial beam and the non-delayed partial beam being identical withregard to shape and size because the mirrors 12 and 14 bring about a 1:1imaging of the light beam at the beam splitter area 68 onto the beamcombining area 70.

As is illustrated in FIG. 3 c), the light beam 11 that is partly coupledinto the delay module 52 passes from the beam splitter area 68 orcoupling-in area 18, which coincide here, through the delay module 52and is folded at the mirrors 12 and 14 in the order of the points a toh. At the coupling-out area 20 or beam combining area 70, the delayedpartial beam is then coupled out of the delay module 52.

As in the case of the exemplary embodiment in accordance with FIG. 2,the delayed partial beam of the light beam 11 thus passes back and fortheight times between the mirrors 12 and 14 and correspondingly has adelay which approximately corresponds to eight times the mirror distanceD between the mirrors 12 and 14.

In the case of the exemplary embodiments in accordance with FIGS. 2 and3, the prism 38 and the prisms 64 and 66 are in each case arranged insuch a way that their hypotenuses are perpendicular to the respectiveincident light beam 11, with the result that no refraction occurs at thehypotenuse. The hypotenuse may also be provided with reflection-reducingcoatings in order to avoid light losses through undesirable reflection.

In this case, the reflection at the reflective areas 34, 36 and 56 to 62may be based solely on total reflection, or the corresponding areas mayalso be provided with reflective coatings.

Instead of the two individual prisms 64 and 66 in the exemplaryembodiment in accordance with FIG. 3, it is also possible to use asingle component, for example a double retroprism 72, illustrated inFIG. 7.

FIG. 4 illustrates a further exemplary embodiment of a pulsemultiplication or elongation module 80, which has a delay module 82,which is in turn based on the delay module 10 in FIG. 1 but differs fromthe previous exemplary embodiments by virtue of a modified opticalarrangement 84.

The optical arrangement 84 has a plurality of refractive areas, fourrefractive areas 86, 88, 90, 92 in the exemplary embodiment shown.

The refractive areas 86 to 92 are formed by the surfaces of a rhombicprism 94, the tilting of the refractive areas 86 and 90, and 88 and 92,relative to the beam direction preferably corresponding to the Brewsterangle, as a result of which reflection losses at the areas 86 to 92 canbe minimized, and can even be precluded when using polarized light.

From the refractive areas 86 to 92, the areas 86 and 88 form a pairwhich axially offsets the light beam 11, but without altering thedirection of propagation of the light beam 11, and the areas 90 and 92likewise form an axially offsetting pair of refractive areas.

The pulse multiplication or elongation module 80 furthermore has a beamsplitter area 96 and a beam combining area 98, which coincide with thecoupling-in area 18 and the coupling-out area 20 as in the case of theprevious exemplary embodiment.

Proceeding from the coupling-in area 18 or beam splitter area 96, a partof the coupled-in light beam 11 is coupled into the delay distance ofthe delay module 81. From the coupling-in area 18, the light beam 11passes to the location a on the first mirror 12, is reflected there tothe location b on the second mirror 14, from there to the location c onthe first mirror, and from there to the location d on the second mirror14. The light beam is then axially offset at the pair of refractiveareas 86, 88, with the result that it initially does not impinge on thebeam combining area 98, but rather passes to the location e on the firstmirror 12, and is reflected from there to f on the second mirror 14,from there to the location g on the first mirror 12 and from there tothe location h on the second mirror 14. From there the light beam passesthrough the pair of refractive areas 90 and 92 and is axially offsetthere into the original position again, and subsequently impinges on thecoupling-out area 20 or beam combining area 98, with the result that thedelayed partial beam is combined with the non-delayed partial beam ofthe light beam 11. Here as well, the delayed partial beam is unchangedrelative to the non-delayed partial beam in respect of size and shape.

Given this choice of optical arrangement 84, the light beam 84, asillustrated in FIG. 4 b), impinges on the mirrors 12 and 14 at thepoints a to h, that is to say on each mirror 12 and 14 at four locations(FIG. 4 b) illustrates the points d, h, f, b on the second mirror 14)which lie on a straight line, that is to say that the beam folding inthe delay module 82 is not three-dimensional, but rather onlytwo-dimensional. In FIG. 4 b) BS denotes the beam splitter area 96 orbeam combining area 98.

FIG. 6 illustrates the prism 94 in isolation.

Generally, optical arrangements which axially offset the light beambetween the mirrors 12 and 14 without any change in direction or axiallyoffset the light beam with a reversal of direction can be combined withone another in any desired arrangements. In this way, the entire mirrorarea of the spherical mirrors 12 and 14 can be used to delay the lightbeam by 2 N-fold folding. The three-dimensional folding in accordancewith the exemplary embodiments in FIGS. 2 and 3 has the advantage inthis case that a larger region of the mirror area of the mirrors 12 and14 can be used for folding than in the case of two-dimensional folding.

FIG. 5 illustrates by way of example the three-dimensional equivalent tothe beam folding in accordance with FIG. 4 b).

FIG. 8 furthermore illustrates as an example an optical arrangement fora pulse multiplication or elongation module in which a delay inaccordance with FIG. 1 with four circulations is combined with a delaywith eight circulations in accordance with FIG. 3. Consequently, theresult is twelve circulations of the light beam between the just twomirrors 12 and 14, and the light beam is correspondingly reflected sixtimes at each of the mirrors 12 and 14, as is illustrated with six spotsin FIG. 8. Consequently, such a pulse multiplication or elongationmodule merely requires the two mirrors 12 and 14, two beam splitters BS₁and BS₂ and, by way of example two prisms P₁, P₂. In this way, by way ofexample, a 30 ns pulse can be elongated to more than 140 ns. Byinserting further optical elements, significantly greater delays orpulse elongations are also possible with one and the same modulecomprising the mirrors 12 and 14.

Whereas in the case of the exemplary embodiments in accordance withFIGS. 3 and 4 the beam splitters and beam combiners are integrated inthe delay module, it is also possible, however, in accordance with FIG.9, to combine a pure delay module, for example the delay module 30 inFIG. 2, with an external beam splitter area 100 and an external beamcombining area 102. In accordance with FIG. 9, it is possible forexample to combine the delay line described in the document EP 1 069 453A2, the content of which is expressly incorporated by reference here,with additional mirrors 104 to 108 with the delay module 30 in FIG. 2,the latter then not having a dedicated beam splitter device.

1. An optical delay module for lengthening the propagation path of alight beam, comprising: a first mirror and a second mirror, said firstand second mirrors being situated opposite one another at a mirrordistance from one another; a coupling-in area for coupling said lightbeam into a space between said first and second mirrors, and acoupling-out area for coupling the light beam out of said space betweensaid first and second mirrors, said propagation path of said light beambetween said coupling-in area and said coupling-out area correspondingat least approximately to quadruple said mirror distance; at least oneoptical arrangement arranged between said first and second mirrors, saidoptical arrangement being arranged to transfer said light beam withoutmasking out of beam parts between said first and second mirrors in sucha way that said propagation path of said light beam between saidcoupling-in area and said coupling-out area corresponds approximately to2-N times said mirror distance, where N is an integer >2.
 2. The opticaldelay module of claim 1, wherein said optical arrangement transfers saidlight beam in such a way that said light beam is reflected at said firstand said second mirror at in each case at least three differentlocations.
 3. The delay module of claim 1, wherein said opticalarrangement transfers said light beam in such a way that said light beamis reflected at said first and said second mirror at least threedifferent locations which lie in a common plane.
 4. The delay module ofclaim 1, wherein said optical arrangement transfers said light beam insuch a way that said light beam is reflected at each mirror at at leastthree different locations which do not lie on a straight line.
 5. Thedelay module of claim 1, wherein said optical arrangement transfers saidlight beam at least once with reversal of a propagation direction ofsaid light beam in an axially offset manner.
 6. The delay module ofclaim 1, wherein said optical arrangement transfers said light beam atleast once with maintenance of a propagation direction in an axiallyoffset manner.
 7. The delay module of claim 1, wherein said opticalarrangement has at least two reflective areas which are arrangedrelative to one another in such a way that said light beam isretroreflected with an axial offset.
 8. The delay module of claim 7,wherein said at least two reflective areas are at an angle ofapproximately 90° with respect to one another.
 9. The delay module ofclaim 1, wherein said optical arrangement has at least one 90° prismwhose two catheti have reflective areas.
 10. The delay module of claim9, wherein said hypotenuse of said prism is perpendicular to said lightbeam when being incident on and emerging from said prism.
 11. The delaymodule of claim 1, wherein said optical arrangement has at least tworeflective areas which are arranged relative to one another in such away that said light beam is retroreflected with an axial offset, andwherein said at least two reflective areas are formed by at least twomirrors.
 12. The delay module of claim 1, wherein said opticalarrangement has at least two reflective areas which are arrangedrelative to one another in such a way that said light beam isretroreflected with an axial offset, and wherein said coupling-in areais formed by a rear side of one reflective area of said opticalarrangement.
 13. The delay module of claim 1, wherein said opticalarrangement has at least two reflective areas which are arrangedrelative to one another in such a way that said light beam isretroreflected with an axial offset, and wherein said coupling-out areais formed by a rear side of said at least one second reflective area ofsaid optical arrangement.
 14. The delay module of claim 1, wherein saidoptical arrangement has at least four reflective areas, in each case twoof said reflective areas being arranged with respect to one another insuch a way that they retroreflect said light beam with an axial offset.15. The delay module of claim 14, wherein said optical arrangement hasat least two 90° prisms whose in each case two catheti form said in eachcase two reflective areas, said prisms being arranged with their 90°angles facing one another.
 16. The delay module of claim 14, whereinsaid optical arrangement has at least one double retro prism which isformed in such a way that said light beam is retro-reflected on anoutward path and a return path in each case with an axial offset. 17.The delay module of claim 1, wherein said optical arrangement has atleast two reflective areas which are arranged relative to one another insuch a way that said light beam is retroreflected with an axial offset,and wherein said at least two reflective areas are arranged in a planeoutside a plane containing said common axis of symmetry of said firstand second mirrors.
 18. The delay module of claim 1, wherein saidoptical arrangement has at least two refractive areas through which saidlight beam is axially offset upon passing through.
 19. The delay moduleof claim 1, wherein said optical arrangement has at least fourrefractive areas, of which two areas in each case are parallel to oneanother.
 20. The delay module of claim 19, wherein said at least tworefractive areas are arranged at the Brewster angle with respect to saidlight beam.
 21. An optical pulse multiplication or elongation module,having at least one beam splitter area, and having at least one beamcombining area, and further comprising at least one optical delaymodule, said at least one optical delay module comprising a first mirrorand a second mirror,; said first and second mirrors being situatedopposite one another at a mirror distance from one another; acoupling-in area for coupling said light beam into a space between saidfirst and second mirrors, and a coupling-out area for coupling the lightbeam out of said space between said first and second mirrors, saidpropagation path of said light beam between said coupling-in area andsaid coupling-out area corresponding at least approximately to quadruplesaid mirror distance; at least one optical arrangement arranged betweensaid first and second mirrors, said optical arrangement being arrangedto transfer said light beam masking out of beam parts between said firstand second mirrors in such a way that said propagation path of saidlight beam between said coupling-in area and said coupling-out areacorresponds approximately to 2-N times said mirror distance, where N isan integer >2.
 22. The pulse multiplication or elongation module ofclaim 21, wherein said at least one beam splitter area and said at leastone beam combining area essentially coincide.
 23. The pulsemultiplication or elongation module of claim 21, wherein said at leastone beam splitter area coincides with said coupling-in area and said atleast one beam combining area coincides with said coupling-out area. 24.The pulse multiplication or elongation module of claim 21, wherein atleast one of said at least one beam splitter area and said at least onebeam combining area is separated from at least one of said coupling-inarea and said coupling-out area.
 25. A semiconductor lithography system,comprising an optical delay module for lengthening the propagation pathof a light beam, comprising a first mirror and a second mirror, saidfirst and second mirrors being situated opposite one another at a mirrordistance from one another a coupling-in area for coupling said lightbeam into a space between said first and second mirrors, and acoupling-out area for coupling the light beam out of said space betweensaid first and second mirrors, said propagation path of said light beambetween said coupling-in area and said coupling-out area correspondingat least approximately to quadruple said mirror distance; at least oneoptical arrangement arranged between said first and second mirrors, saidoptical arrangement being arranged to transfer said light beam withoutmasking out of beam parts between said first and second mirrors in sucha way that said propagation path of said light beam between saidcoupling-in area and said coupling-out area corresponds approximately to2 N times said mirror distance, where N is an integer >2.
 26. Asemiconductor lithography system, comprising an optical pulsemultiplication or elongation module, having at least one beam splitterarea, and having at least one beam combining area, further comprising atleast one optical delay module, said optical delay module comprising afirst mirror and a second mirror, said first and second mirrors beingsituated opposite one another at a mirror distance from one another acoupling-in area for coupling said light beam into a space between saidfirst and second mirrors, and a coupling-out area for coupling the lightbeam out of said space between said first and second mirrors, saidpropagation path of said light beam between said coupling-in area andsaid coupling-out area corresponding at least approximately to quadruplesaid mirror distance; at least one optical arrangement arranged betweensaid first and second mirrors, said optical arrangement being arrangedto transfer said light beam without masking out of beam parts betweensaid first and second mirrors in such a way that said propagation pathof said light beam between said coupling-in area and said coupling-outarea corresponds approximately to 2 N times said mirror distance, whereN is an integer >2.